The present invention relates to a leveling device, and in particular, to a leveling device for correcting defective shapes of a strip and to a leveling method therefor.
A conventional leveling device is shown in Fig. 1 of Japanese Patent Unexamined Publication No. 63-149015. As shown there, the leveling device is mainly composed of a tension leveler, inlet side bridle rolls located at the inlet side of the tension leveler, and outlet side bridle rolls located at the outlet side of the same. A strip is leveled by repeatedly receiving bending actions as being tensioned by means of the inlet side and outlet side bridle rolls.
In the above-mentioned leveling device, however, chatter marks are apt to be generated on the surface of the strip, thereby deteriorating the quality of the products. Especially, this phenomenon is undesirable in the present time where the requirement for flatness is strict. Here, the term "chatter mark" is used for expressing a striped pattern extending in the crosswise direction of the strip with a small pitch on the strip surface, which has, when viewed in detail, a wave-like shape having small wave heights.
A conventional means for preventing the generation of chatter marks is disclosed in Japanese Patent Unexamined Publication No. 58-151918, where a roll unit is composed of small-diametral rolls and large-diametral rolls located at the front and rear sides of the small-diametral rolls with the strip interposed between the small-diametral rolls and the large-diametral rolls, and a plurality of these roll units are arranged on a line.
In the above-mentioned conventional art, since the winding angle of the small-diametral rolls is excessive, curvature fluctuation of the strip is generated due to the vibration of the strip, thereby generating the chatter marks. As a solution for suppressing the curvature fluctuation, the above-mentioned roll arrangement has been developed.
In the above-mentioned prior art, however, no consideration is paid to the fact that the chatter marks can be prevented by decreasing the passing speed of the strip to a very low level, for example, as low as 10 m/min.
In consequence, the generation of chatter marks can not be prevented by merely arranging great-diametral rolls in the front and rear sides of the small-diametral rolls, especially, in case the flatness requirement for the strip is strict.
On the other hand, Japanese Patent Unexamined Publication No. 56-128623 discloses an arrangement where a tension distribution control device movable in the crosswise direction of the plate, is provided between an inlet side bridle roll or an outlet side bridle roll and a tension leveler.
For obtaining an excellent shape control of the strip, the elongation of the strip in the crosswise direction is controlled by applying a suitable tension distribution to the strip in the same direction.
In the above-mentioned prior art, however, nothing is referred to with respect to the prevention of chatter marks. Further, it is clear that the chatter marks can not be prevented by merely providing the above-mentioned tension distribution control device, for the reason below.
Namely, in this tension distribution control device, since the tension distribution is applied along the widthwise direction of the strip, the influence of the tension distribution control device on the strip along the widthwise direction varies in the widthwise directions, and accordingly, the chatter marks can not be prevented.
Further, as shown in Fig. 6 of the above-mentioned Japanese Patent Unexamined Publication No. 56-128623, since the roll has a tapered portion, it is clear that the influence varies in the widthwise direction of the strip.
In addition, this tension distribution control device can be applied only to case the strip is formed with rims along the side edges of the strip, and can not be applied to a usual case.